BELGRADE – Though no one was seriously hurt in a landmark gay-rights march here on October 10, the violence between ultranationalist protesters and police that engulfed the Serbian capital threatens to overshadow a visit by U.S. Secretary of State Hillary Clinton.

Nearly 150 people -- mostly police officers -- were wounded in the rioting, which pitted some 6,000 protesters against nearly that many police and internal security officers. About 250 were arrested in the aftermath of the violence, which saw roving gangs wreak havoc across Belgrade, as entire sections of the city effectively became no-go zones.

The effects of the rioting were visible on the streets the next day in the form of broken shop windows and anti-EU graffiti. Protesters burned the headquarters of the ruling Democratic Party, whose leader, President Boris Tadic, vocally supported the parade. The city government has estimated the damage at over 1 million euros ($1.4 million).

While organizers of the gay-pride parade have commended police for ensuring the safety of participants, others are calling attention to what they claim was a failure by the government to adequately prepare for the violence -- the worst domestic unrest the Balkan country has seen in over a decade.

Security expert Zoran Dragisic told the local "Press" newspaper that “one cannot criticize ordinary policemen, but the major mistake was made by the BIA [Security Information Agency]."

This is not the first time that far-right, ultranationalist groups have sparked violence in Serbia. In 2008, several hundred protesters attacked the U.S. Embassy in Belgrade after Washington announced its recognition of the erstwhile Serbian province of Kosovo. Later that year, similar elements rioted when Bosnian Serb wartime leader Radovan Karadzic, wanted in The Hague for war crimes, was arrested.

WATCH: Video of the clashes and gay-pride parade, including an interview with Mary Burce Warlick, the U.S. ambassador to Serbia:

“After all these experiences, BIA didn’t manage to find the guys who financed all this. ... The state cannot just stop by arresting those people [on October 10], because they were just manipulated kids. It has to bring the instigators to justice," Dragisic said.

The police did not seem to be prepared for so many rioters, leading many here to believe that the widespread havoc was the result of an intelligence failure and the inability of the security forces to penetrate far-right organizations with undercover operatives or to cultivate informants.

A spokesman for the BIA, Jovan Stojic, refused to comment to the newspaper.

The top items on the agenda for the Clinton visit will be Serbia’s EU accession process, encouraging Serbia to negotiate directly with Kosovo, and to pressure Belgrade to apprehend accused Serbian war criminal Ratko Mladic. Clinton is due to arrive late on October 11 in Sarajevo and will continue to Belgrade on October 12 and Pristina on October 13.

Though the Serbian government won plaudits from Western embassies for its cooperation with the gay-rights march -- the U.S. ambassador to Serbia, Mary Burce Warlick, who attended a pre-march rally, told RFE/RL that the United States “is very pleased with the government’s strong support in terms of security measures for the event” -- the intensity of the violence demonstrated the power of the ultranationalist right to cause instability.

Though the impetus for the October 10 riots was the gay-rights march, much of the rhetoric from protesters took on a nationalist and anti-Western cast. At a rally on October 9, several hundred protestors gathered to call on the government to cancel the parade, with one speaker blaming it for failing to respect “the territorial integrity of Serbia.”

Gay-rights acivists march under police protection in Belgrade.

“They have a real impact,” says Maja Milic, director of the Youth Initiative for Human Rights, a Belgrade-based nongovernmental organization. “They learned that they are powerful. That’s what they learned from [the October 10 protests].”

Given their success in shutting down much of Belgrade, Milic worries that the same ultranationalist groups may return to the streets on October 12 in protest of Clinton’s visit. Adding to worries is that Clinton is not particularly liked here, especially among the nationalist, pro-"Greater Serbia” far right, given her outspoken support for the 1999 NATO bombing campaign, which put an end to former Serbian President Slobodan Milosevic’s ethnic-cleansing campaign.

Milic says that were Serbia to enter into negotiations with Kosovo – even while declining to formally recognize its independence – it could provide a boost to the country’s nationalists and possibly bring about the fall of Tadic’s already precarious coalition government (which has 128 seats in a 250-member parliament).

Milic says that the popular response to the October 10 parade – which ran the gamut from indifference to passive and active hostility – shows that Serbia has a long way to go before it will ever be ready to join the EU. And she thinks that Clinton should make this reality clear during her visit.

“I hope she will say that there’s a big job in front of us as a people, a society, and government,” Milic says.

James Kirchick is writer at large with Radio Free Europe/Radio Liberty